reshape base functionDF.to.longDT)DF.to.long(df_wide)data.frame in wide formatdata.frame object in long formatAll covariates that appear fewer than range(t) times are imputed with NA for missing time-points.
Observations with all NA's for all time-varying covariates are removed.
When removing NA's the time-varying covariates that are attributes (attnames) are not considered.